The present invention relates to an epoxy resin molding material for sealing electronic parts which is excellent in thermal shock resistance, reflow soldering resistance and moldability, and to a semiconductor device sealed with the epoxy resin molding material, particularly to a plastic-packaged LSI for surface mounting.
Epoxy resin molding materials have been widely used in large quantities for sealing electronic parts, such as transistors, IC, etc. The reason is that epoxy resins are well-balanced in various properties including electric properties, thermal resistance, mechanical strength and adhesiveness to inserts. Particularly, combinations of o-cresol novolac epoxy resins and phenol novolac hardeners are especially well-balanced in these properties, and have been used as the main base resins of molding materials for IC-sealing.
However, the recent downsizing and thinning of packages of electronic parts, typically of IC packages, have caused cracking of such packages on cyclic cooling and heating and demand further improvement in thermal shock resistance.
The conventional means of improving the thermal shock resistance of epoxy resin molding materials are
(1) dispersing liquid silicones in epoxy resin molding materials; PA1 (2) the method disclosed in Japanese Patent Application Kokai Koho (Laid-open) No. 1-272620, wherein epoxy resins or hardeners are previously modified with siloxane compounds; and PA1 (3) the methods disclosed in Japanese Patent Application Kokai Koho (Laid-open) Nos. 61-185527, 62-93962, 62-147749 and 5-175369, wherein epoxy resins are modified with silicone polymer powder. PA1 (A) an epoxy resin having at least two epoxy groups per molecule, PA1 (B) a compound having at least two phenolic hydroxyl groups per molecule and PA1 (C) a powder which
The method (1) lowers the cracking resistance during reflow soldering processes and marking properties, and also deteriorates the appearance of molded products due to the bleeding of the liquid silicones. The method (2) tends to lower glass transition temperature, thereby deteriorating the thermal resistance of packages. Every method (3), namely the modification with silicone polymer powder, successively lower the elastic moduli of epoxy resin compositions and decreases the stress generated on the interface between IC elements and epoxy resin molding materials. However, the methods disclosed in Japanese Patent Application Kokai Koho (Laid-open) Nos. 61-185527 and 5-175369, wherein solid silicones are dispersed, have a shortcoming of lowering the breaking point and elongation at break of resulting epoxy resin molding materials. Such a shortcoming seems to be caused by the poor affinity between the silicone particles and the epoxy resins. As disclosed in Japanese Patent Application Kokai Koho (Laid-open) Nos. 62-93962 and 62-147749, coating the surface of silicone particles with resins which are compatible with epoxy resins improves the affinity, and obviates to some degree the decrease in strength and elongation. However, the cores of the particles produced by these methods are liquid silicones or contain liquid silicones, and there arise various troubles due to the presence of the liquid silicones. The particular troubles made by such liquid components are the deterioration of the marking properties of the surface of packaged IC and the debonding and falling of ICs from wiring boards on which the ICs have been temporarily fixed with adhesives for mounting.